1. Field of the Invention
The present invention concerns a method of forming wirings. The present invention can be utilized as a method of forming metal wirings, for example, in electronic materials (such as semiconductor device).
2. Description of the Prior Art
Wiring structures, for example, wirings for semiconductor devices such as LSI in the prior art are sometimes formed by forming films at a high temperature. For instance, Al series materials have often been used in view of their low resistivity and easy fabricability, and Al series alloys have been generally used therefor. The Al series alloys have usually been formed by a sputtering method, in which sputtering under heating, so-called, a high temperature sputtering method has also been used.
Among the Al series alloys, Si-containing alloy materials such as Al--Si or Al--Si--Cu have often been used with an aim of preventing penetration of Al in a portion of contact with a Si diffusion layer in a case where the underlying material is a silicon substrate. That is, Si-containing Al alloys comprise about 1 wt % of Si and, by incorporating Si in an amount generally greater than the solid solubilization limit (for example, 1 wt %) in Al, diffusion of Si from the Si substrate into Al in the portion of contact is prevented thereby suppressing Al from intruding into the Si substrate.
As the size of the LSI devices has become finer in recent years, the size and the shape of a wiring width and a connection hole have been also, in which a problem of Si nodules has become serious in view of the reliability of the wirings. That is, since the width of wirings is reduced in a portion in which Si nodules occur in the wirings, it may be a worry of wiring disconnection due to increase of wiring resistivity or local increase in the current density. FIG. 26(a), (b) and FIG. 27(a), (b) show Al--Si wiring 30 in which Si nodule 14 occurs. As can be seen from cross sectional views of FIG. 26(b) and FIG. 27(b), as well as from FIG. 28 corresponding to FIG. 25, a Si nodule 14 occurs biting into the wiring 30 to reduce the wiring width in a portion shown by a reference numeral 15.
On the other hand, it has been known that the size and the number of Si nodules depend particularly on the heating temperature for a substrate upon forming a Al alloy film or heat treatment after the formation of the film such as Al sintering. In view of the above, it has been attempted to reduce the Si nodules by improving and optimizing the heating processes, thereby suppressing the undesired effect on the reliability. However, the Si nodules can not completely be eliminated after all by such a method. With the reasons as described above, there has been demanded for a drastic countermeasure capable of completely suppressing the occurrences of the Si nodules also in a case in which Al--Si is used as the Al series material.
Further, the foregoing problem may arise in any of the cases in the technique for forming wirings by film formation of a Si-containing metal layer.